Merriam-Webster's Collegiate® Dictionary, 11th Edition
SEX
I. noun
Etymology: Middle English, from Latin sexus
Date: 14th century
either of the two major forms of individuals that occur in many species and that are distinguished respectively as female or male especially on the basis of their reproductive organs and structures, the sum of the structural, functional, and behavioral characteristics of organisms that are involved in reproduction marked by the union of gametes and that distinguish males and females,
3. sexually motivated phenomena or behavior, sexual intercourse , genitalia ,
II. transitive verb
Date: 1884
to identify the sex of ,
2. to increase the sexual appeal of, to arouse the sexual desires of